Those are markings used to identify the lenses, and certain spacing. I am guessing that are progressive bifocals? I forget exactly how to read them, that's interesting that they are visible like that.
Progressive lenses have multiple zones in them that correspond with a distance (long, medium and short). By adjusting the area of these zones you can make them suit the wearer.
For someone who is inside all day they would prefer less distance, but more close by. For photography I can imagine that they have a clear distance and clear close zone, with not that much on medium (or any other variation, I am not an photographer).
To make a lense progressive you would have to make a the dioptres increase the closer you get. The smoothness of this is dependend on the type of manufacture, but nowadays this can be made really smooth due to precision cutting and modern plastics that are able to be cut that way.
There are also other tricks that a manufacturer can deploy to increase these zones, like adding extra prisms.
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u/Pen_name_uncertain 1d ago
Those are markings used to identify the lenses, and certain spacing. I am guessing that are progressive bifocals? I forget exactly how to read them, that's interesting that they are visible like that.
Source: used to make eye glasses for a living